The Strong Duschinsky Effect and the Intensity of Transitions in Non-Totally Symmetric Vibrations in the Electronic Spectra of Polyatomic Molecules
The effect of strong Duschinsky type mixing of two normal coordinates Q1 and Q2 on the intensity of transitions in non-totally symmetric vibrations in electronic spectra is examined. Using a Fermi resonance type theory, expressions are derived for the intensity of transitions such as 1(1)02(0)1 and 1(1)02(1)0 which gain significant intensity when mixing of coordinates is strong. The results are applied to the 288-nm electronic spectrum of styrene, the 370-nm spectrum of tropolone, and the 281-nm spectrum of 1,4-benzodioxan, all of which provide examples of strong mixing between a pair of normal coordinates. In some cases the theoretical predictions are in general agreement with the observed intensity pattern, if a suitable choice is made of the relevant mixing coefficient. In others there is a divergence which may be related to the importance of other factors such as electrical and mechanical anharmonicity. Copyright 1998 Academic Press. Copyright 1998Academic Press
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